Add initial work on unification in desugarer
Merge branch 'unify' into unify-ds

Conflicts:
	sugar/Desugar.hs
Initial work on desugaring with type inference
Add occurs check
Print the goal type in holes
Work on unification
Fix tyRenameList bug
Final stab at this unification attempt

I have a solution in mind!
unification fixes
Merge branch 'unify'